commit eeb8a7e8 upstream.

when multiport is off, virtio console invokes config access from irq
context, config access is blocking on s390.
Fix this up by scheduling work from config irq - similar to what we do
for multiport configs.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
[bwh: Backported to 3.2:
 - Adjust context
 - Drop changes to virtcons_freeze()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>